The polyurethane-forming polyaddition reaction between polyhydroxyl compounds and polyisocyanates, particularly aliphatic and alicyclic polyisocyanates, normally involves a two-component system. One of the components consists of a polyfunctional isocyanate. The second component contains a polyol, optionally a blowing agent together with further modifying agents and additives, and suitable catalysis to obtain a reaction between components which is fast enough for industrial purposes. This second component is normally used in the form of a prepared mixture by the processor, i.e., it is prepared weeks or months before processing.
It is known that both divalent and also tetravalent tin compounds, divalent lead and trivalent bismuth compounds are effective catalysts for the isocyanate addition reaction. It is further known that activator combinations of metal compounds and amine-containing catalysts selected from, for example, tertiary amines or amidines, such as triethyl amine, triethylene diamine (diazabicyclooctane or "Dabco.RTM.") or diazabicycloundecene (DBU), or other non-amine catalysts, for example, basic catalysts, may also be used for this purpose. Examples of the metal compounds used include the bis-carboxylates of dialkyl tin compounds, such as di-(n-butyl)-tin dilaurate, or the bis-mercaptides of dialkyl tin compounds, such as dimethyl tin bis-(laurylmercaptide), metal acetyl acetonates, such as Fe(II) acetyl acetonate, Fe(III) acetyl acetonate, dibutyl tin acetyl acetonate and lead (II) acetyl acetonate and other lead compounds, such as lead di-(2-ethylhexanoate), or bismuth compounds, such as, for example, bismuth tri-(2-ethylhexanoate).
Some of the most preferred catalysts include tin II) bis-(2-ethylhexanoate), dibutyl tin di-(laurylmercaptide), dibutyl tin di-laurate (DBTL), dialkyl tin di-(thioglycolic acid esters), such as, for example, M&T-C 131, lead(II) di-(2-ethylhexanoate), lead (II) dinaphthenate and bismuth tri-(2-ethylhexanoate) or bismuth tri-(thiododecyl). Unfortunately, these catalysts, like most other members of these classes of tin, lead and bismuth compounds, undergo a considerable loss of activity when incorporated in a polyol mixture containing one or more short-to-long-chain, linear or branched, polyols, optionally in admixture with other compounds containing NCO-reactive groups (such as, for example, polyamines), blowing agents, additives such as cell stabilizers, heat and light stabilizers and non-metallic co-catalysts.
This loss of activity involves disadvantages from the point of view of practical application.
German Offenlegungsschrift No. 2,722,658 proposes, as storable tin gel catalysts, compounds corresponding to the following general formulae, R.sub.2 Sn (SCN).sub.2, [R.sub.2 Sn(SCN)].sub.2 O, [R.sub.2 Sn(SCN)].sub.2 S, (R.sub.2 SnX).sub.2 S and R.sub.2 SnS, wherein R represents a hydrocarbon and X represents chlorine, bromine or iodine. The disadvantages of these compounds, however, include their poor solubility and their low activity which makes them unsuitable for most polyurethane plastics. In this reference, these catalysts are used in quantities of from 0.1 to 10 parts, by weight, per 100 g of polyol, the lower limit of this range actually lying above the concentration in which the tin catalysts are normally used.
The object of the present invention is to provide a new, storable mixture of polyol and metal catalysts, which catalysts are stable in their activity and which, in addition, are intended to be readily soluble in the polyol component. Another object of the present invention is to provide a process for the production of polyurethanes using these catalysts.
Surprisingly, these objects could be achieved by using tin compounds corresponding to the following general formula as the metal catalysts.